Precast concrete panels are well established within the art and offer many advantages for building construction which will not be discussed here. The most notable drawback of this building system is the large thermal mass of the concrete exposed to the ambient temperatures. Improvements addressed this issue in the 1970's by the invention of the sandwich panel (U.S. Pat. No. 4,974,381). This improvement places a layer of insulation between a structural concrete inner layer and a non-structural concrete outer layer during the casting of the panel and then erecting this entire composite-like construction/unit as a panel.
Existing techniques to manufacture precast sandwich panels off site consist of pouring concrete into formwork containing reinforcing materials which moulds the concrete into the desired panel shape. Forms can be customized prior to each concrete pour with the insertion of window or door frames. Next a layer of insulation is placed on top of the first layer of concrete. Finally, a second layer of concrete is poured on top of the insulation containing reinforcing materials. A major design consideration is how to achieve a high shear stiffness and limit differential slip between the three layers to achieve optimal composite strength. To satisfy this requirement, connectors are inserted through the insulating layer to bond with the concrete in both layers. Whenever thermally conductive materials are utilized as connectors it generates thermal draws greatly reducing the panel's overall insulating properties.
In prior art, connecting systems are generally narrow or slender providing little bending stiffness. Simply increasing the amount inserted or dimension of materials does not increase the strength of the connection. As well, they are inserted perpendicular within the panel and are not well suited to stiffening the panel against longitudinal bending.
According to the new energy code, NEBC 2011, being implemented within the province of Manitoba as of December 2014, the effective R-value required for our climatic area is R-27. Additionally, the specific type of insulation used in our manufacturing of panels, poly isocyanurate, is being downgraded from R-7 to R 5.6.
Therefore, the primary objective of the present invention is to manufacture a sandwich panel with an improved effective R value while maintaining sufficient strength. To achieve this, the insulation layer must be increased in thickness and thermal leakage must be minimized and improved connectors are required to span the increased thickness of the insulation layer.
Another objective of this present invention is to provide a panel connector which achieves one or more of the following design features: be made of non-thermally conductive material, be of sufficient length to bridge the thick insulation layer, provide sufficient strength to the panel for lifting and reduced shearing, be readily accessible, and allow for design flexibility (panel width and length, differing insulation thicknesses and vestibulation placement).